1. Field of the Invention
The present invention relates to a laser radar apparatus, and in particular, to a laser radar apparatus that uses a laser beam to detect the distance and direction of an object to be detected.
2. Description of the Related Art
A conventional laser radar apparatus is disclosed by Japanese Patent Publication No. 2789741. The apparatus disclosed by this publication is provided with a laser beam generator, a detector, and an optical isolator through which the laser beam is transmitted. The laser beam generator generates a laser beam and the optical isolator is located on the optical axis of the laser beam from the generator to reflect a reflected light toward the detector that detects reflected light from an object to be detected. In addition, a concave mirror is located on the optical axis of the laser beam such that the concave mirror rotates on its central axis along the optical axis direction of the laser beam. This concave mirror reflects not only the incident laser beam into the air but also the reflected light from the object to be detected toward the isolator, so that horizontal scanning can be performed over 360 degrees.
However, in the case of the technique according to the above publication, the 360-degree horizontal scanning, which is performed by rotating the concave mirror, is confronted with a drawback. As described, the horizontal scanning over 360 degrees makes it possible to detect the whole surrounding of the apparatus by scanning the whole angular detection range (scanning range on the laser beam). However, there is a problem that the detection range is limited to a planer range. Specifically, the laser beam that has been reflected specially from the concave mirror is obliged to scan a given planar (scanned planar), resulting in that regions which are outside the scanned planar cannot be scanned. That is, if objects are shifted from the scanned planar, the objects cannot be detected. In addition, even when the objects exist in the scanned planar, it is impossible to grasp the presence of the objects in the three-dimensional manner.